Due to stricter regulations, there is a significant amount of research being conducted to identify and produce organofluorine compounds having a much lower global warming potential (GWP) and zero or near zero ozone depletion potential (ODP). For example, hydrofluoroolefins (HFOs) including HFO-1234yf (1,1,1,2-tetrafluoropropene), HFO-1234ze (1,1,1,3-tetrafluoropropene), and HFO-1243zf (1,1,1-trifluoropropene), and hydrochlorofluoroolefins (HCFOs) such as HCFO-1233zd (1,1,1-trifluoro-3-chloropropene) and HCFO-1233xf (1,1,1-trifluoro-2-chloropropene) have been identified as fluorocarbons having a lower GWP, and therefore are considered to be non-greenhouse gases. Additionally, the ODP of those compounds is zero or negligible. HFO-1234yf, HFO-1234ze, and HCFO-1233zd, which are environmentally acceptable, have also been found to have lower flammability, acceptable toxicity, and good performance. Therefore, these products are under consideration by the industry as refrigerants or refrigerant components of a blend, foam blowing agents, aerosol propellants, and solvents for metal degreasing.
However, the production of these and other organofluorine compounds often require substantial separation steps to isolate the compounds from other components present in the reaction product, including unreacted feedstock, undesirable byproducts, and coproducts.
Production of organofluorine compounds often results in the formation of other organofluorine compounds, organochlorines, and chlorofluorocarbons (collectively referred to herein as “coproducts of organofluorine production” or simply “coproducts”), as both intermediate products and coproducts that appear in the final reaction mixture. For example, production of HFO-1234yf often forms other coproducts, such as HCFC-244bb (2-chloro-1,1,1,2-tetrafluoropropane), HFC-245cb (1,1,1,2,2-pentafluoropropane), and HFO-1233xf. Production of HCFO-1233zd and HFO-1234ze often forms a reaction mixture comprising unsaturated coproducts, such as cis and trans HCFO-1232zd (c/t-2,3-dichloro-3,3-difluoropropene), cis and trans HCFO-1231zd (c/t-1,3,3-trichloro-2-fluoropropene), and HFO-1243zf, and saturated coproducts, such as HFC-245fa (1,1,1,3,3-pentafluoropropane), HCFC-244fa (3-chloro-1,1,1,3-tetrafluoropropane), HCFC-243fa (2,2-dichloro-1,1,1-trifluoropropane), HCFC-242fa (1,3,3-trichloro-1,1-difluoropropane), HCFC-241fa (1,1,3,3-tetrachloro-1-fluoropropane), and HCC-240fa (1,1,1,3,3-pentachloropropane). Many of these organofluorine compounds and coproducts of organofluorine production form azeotropes or azeotrope-like mixtures, which further complicates separation of the organofluorine compounds.
Undesirable components of the reaction product mixture may include unreacted hydrogen fluoride (HF), carbon monoxide (CO) and carbon dioxide (CO2), water, and hydrogen chloride (HCl), oxygen, nitrogen, NOx, chlorine and impurities. Many of these organofluorine compounds are known to form an azeotrope or azeotrope-like mixtures with hydrogen fluoride, HF.
In conventional methods, the organofluorine compounds are separated from unreacted HF using separation techniques such as scrubbing, distillation, and phase separation.
In one conventional method, HF is removed from the organofluorine by water scrubbing, which is followed by organic drying and then distillation of the impure organic. The HF is discharged as waste aqueous HF.
In another conventional method, sulfuric acid is used to absorb HF from the organofluorine mixture. The HF is then desorbed, which allows the HF to be recycled back to the fluorination reactor. The use of sulfuric acid is limited because it can lead to unwanted reactions, such as the isomerization of trans-HCFO-1233zd to the toxic cis-HCFO-1233zd.
Other conventional methods include low temperature phase separation, in which an HF-rich phase is removed from an organic-rich phase. The HF-rich phase is then fed to a first azeotropic distillation column to recover the azeotrope as an overhead and pure HF as the bottoms. The organic-rich phase, which includes the organofluorine compound, such as HCFO-1233zd, is fed to a second distillation column to further separate HF from the organofluorine. For example, trans-HCFO-1233zd is removed from the top and cis-HCFO-1233zd is removed from the bottom along with HF.
Another conventional separation method comprises organic extractive distillation, which requires the addition of another solvent which is preferentially extracted with either the organofluorine component or HF. A second distillation is then used to recover the extractant from the organofluorine component or the HF.
Current processes for separating organofluorine compounds from other organofluorine compounds or coproducts of organofluorine production rely on distillation, most often azeotropic distillation. Distillation between certain organofluorine compounds and coproducts becomes increasingly difficult when the boiling points differ by 10° C. or less.
The conventional methods for separating organofluorine compounds are time-consuming and expensive, and, in many cases, involve the use of additional components, which require further separation to form an isolated product.
Membrane separation technology is widely used on many industrial processes such as, for example, gas permeation (e.g. separation of oxygen, nitrogen, helium from air; separation of hydrogen from hydrocarbon such as methane). Liquid separation membranes are used, for example, in the recovery of zinc from wastewater or nickel from electroplating solution. Reverse osmosis is used in desalination plants and in the treatment of waste water to remove impurities.
However, separation membranes have not been used in the fluorochemical industry, such as breaking an azotrope or azeotrope-like or separation of a organofluorine compound from another organofluorine compound, or separation of a organofluorine compound from an HF/organofluorine. A major issue with using membrane separations in the organofluorine industry is the absence of commercial separation membranes compatible with HF and organofluorine products.
Thus, there is a need for separation techniques for the recovery of organofluorine compounds that can be performed more quickly, less expensively, with less energy, and/or without the need for additional chemicals.